Humanity has gone to great lengths to prevent pregnancy. The Ancient Egyptians used mashed crocodile dung as a vaginal suppository. Contraceptive devices deployed in the 19th century included the womb veil, a precursor to the diaphragm, and the Mizpah pessary, a cervical cap made from vulcanised rubber. Early condoms were as thick as the inner tube of a bicycle tyre. Sex in such gear hardly seems worth the effort. Until the pill became widely available in the 1960s, women douched with Lysol, a household disinfectant.

The pill revolutionised women’s reproductive health: it transformed attitudes to sex and allowed women to take control of their bodies. But since its introduction, advances in contraceptive technology have stagnated while hormonal contraceptives continue to have significant shortcomings: side-effects include depression, weight gain, unpredictable bleeding and a higher risk of developing blood clots. Intrauterine devices (IUDs), an effective mechanical alternative to chemicals, can lead to perforation of the uterus and pelvic inflammatory disease.

Now digital technology is offering a less disruptive solution. Earlier this year, Natural Cycles, created by Elina Berglund, formerly a physicist at CERN, and her husband Raoul Scherwizl, became the first fertility-tracking app to be approved for prescription by doctors as a contraceptive device in Britain and the European Union. It draws on the fertility-awareness method, which identifies the crucial stages in a woman’s menstrual cycle through physiological fluctuations. When followed diligently, the method has been shown to be as effective as the pill. Two clinical trials of Natural Cycles reported results in line with these findings. The studies, which surveyed more than 4,000 women aged between 20 and 35, found that the app had an efficacy rate of 99.5%.

Natural Cycles, like most fertility trackers, requires users to take their basal – or resting – temperature each morning (it recom­mends taking your temperature before getting out of bed for accurate results, as urination will alter the reading). Its algorithm combines this measurement with information about cycle irregularities and other temperature fluctuations to pinpoint windows of fertility. A colour-coded calendar helps you schedule your sex life: you can do it unprotected on a green day, as the algorithm has determined that you are not fertile. On a red day, a condom is recommended.

Fertility-tracking apps can be used to help people to conceive as well – you simply target the red days. Natural Cycles can also inform you at a very early stage if you’re pregnant. After a woman ovulates, her temperature rises as more progesterone is released. If conception has been successful, progesterone continues to be secreted to encourage the growth of the fetus. Natural Cycles is able to determine whether the user has been running a temperature for longer than expected. At that point, she is prompted to take a pregnancy test and, once the result has been confirmed, Natural Cycles reconfigures its interface to count down to the baby’s due date.

Birth-control and fertility aids are a lucrative business. A study conducted by Transparency Market Research estimates the current market for contraceptive products is worth $21.5bn. Lots of apps have bloomed in this market but many have been criticised for being little more than glorified period trackers, merely recording menstrual days rather than calculating the window of fertility. Those that do work tend to be better at preventing a pregnancy than at planning one (you can avoid getting pregnant simply by eschewing sex; but having sex at an opportune moment will not guarantee pregnancy as the underlying fertility of participants is a determining factor). Lefa Singleton Norton tested several different fertility trackers before settling on Clue. “It seemed the least garish visually and had the functionality I wanted,” she says. Clue’s user interface has a Scandinavian minimalism: its clean lines are very different from the cutesy pinks and floral motifs of its competitors. In contrast, Eve by Glow seems to have taken its cues from Helen Gurley Brown: its icon for sex with a condom is a wax-tipped banana. Both apps record basal temperatures and menstrual cycles as well as sleep patterns, mood, skin quality, sexual intercourse, cramps and cravings.

It took Singleton Norton about two years to fall pregnant. She used Clue in tandem with the Maybe Baby, a Chapstick-sized microscope that identifies periods of peak ovulation by measuring oestrogen levels in saliva. “Having one place to collect all the data and be able to see patterns in a visual way helped me figure out what my cycles were like, which was pretty important given they didn’t adhere to any formula in ‘trying to conceive’ books or websites,” Singleton Norton says. The app made her feel “more in control”, but “a large part of that was just the sense of having something to do when, as in our case, you can fall pregnant but it just takes for ever.”

It’s clear from talking to users that the psychological effects of these apps are complex. Apps certainly provide less reassurance or certainty than a visit to the doctor; and too much screen time can make some women even more anxious about their fertility status. Critics also worry about the data stored on these apps. How will companies use such highly intimate and sensitive information? Yet many women find that greater knowledge about their bodies is empowering. Kelly Heylen, a gallerist and user of Ovia, yet another app, finds fertility tracking “enlightening”. “I feel much more in control of my reproductive health,” she says. She also believes that the benefits of collecting such data extend beyond the individual. “I quite like the fact that my aggregate data may be used in scientific research, as this research may lead to higher success rates for other women.”

Fertility tech is only going to get better. Natural Cycles’ competitors are finding ways to eliminate human error altogether: the YONO, for instance, tracks your fertility and vital signs while nestled in your ear. And beyond the immediate, practical advantages, the rich, real-time profiles of women these apps provide – demystifying the female body and debunking myths surrounding fertility – are a boon for users and professionals alike. And they’re now at our fingertips.